As shown in FIG. 1, a wireless communication system 10 comprises elements such as client terminal or mobile station 12 and base stations 14. Other network devices which may be employed, such as a mobile switching center, are not shown. In some wireless communication systems there may be only one base station and many client terminals while in some other communication systems such as cellular wireless communication systems there are multiple base stations and a large number of client terminals communicating with each base station.
As illustrated, the communication path from the base station (BS) to the client terminal direction is referred to herein as the downlink (DL) and the communication path from the client terminal to the base station direction is referred to herein as the uplink (UL). In some wireless communication systems the client terminal or mobile station (MS) communicates with the BS in both DL and UL directions. For instance, this is the case in cellular telephone systems. In other wireless communication systems the client terminal communicates with the base stations in only one direction, usually the DL. This may occur in applications such as paging.
The base station to which the client terminal is communicating with is referred to as the serving base station. In some wireless communication systems the serving base station is normally referred to as the serving cell. The terms base station and a cell may be used interchangeably herein. In general, the cells that are in the vicinity of the serving cell are called neighbor cells. Similarly, in some wireless communication systems a neighbor base station is normally referred to as a neighbor cell.
Uplink transmit power control may dynamically change the transmit power to compensate for variations in the instantaneous channel conditions and path loss as a function of the distance between the client terminal and base station. As shown in FIG. 2, the aim of these changes may be to maintain a near constant Signal-to-Noise Ratio (SNR) at the receiver to successfully transmit data without the error probability becoming too high. Under normal conditions, uplink transmit power control increases the power at the transmitter when the radio link experiences poor radio conditions and vice versa.
The uplink transmit power control may be based on a sequence of steps as described below and illustrated in FIG. 3.                1. The signal transmitted by the client terminal is processed at the receiver in the base station. Based on processing of the received signal, the base station may determine whether a change to the uplink transmit power level is necessary.        2. If uplink transmit power level change is necessary at the client terminal, the base station may prepare and schedule an uplink transmit power control message to the client terminal.        3. The uplink transmit power control message may be transmitted from the base station to the client terminal in the downlink.        4. The client terminal may receive and process the uplink transmit power control message.        5. The client terminal may use the received uplink transmit power control message to make change to uplink transmit power level for any future transmissions in the uplink.        
The above process may be repeated on a continual basis to ensure that the client terminal is operating at the optimum uplink transmit power level.
Generally there may be delays involved in the transmission, reception, and processing at both the client terminal and the base station. These delays lead to a certain lag in reacting to the actual propagation channel conditions which may vary fast. For example, the delays for the overall power control loop could be in the order of few tens of milliseconds. Furthermore, in some cases the uplink transmit power control may be an open loop, i.e., there may not be any power control feedback from the base station. For example, such situations may arise during initial transmissions such as Random Access for connection setup from a client terminal. There may be other scenarios where the client terminal may have to transmit in uplink without receiving an uplink transmit power control message after each uplink transmission. The uplink transmit power level may not be optimal in such scenarios.